Method and apparatus for wireless communication in wireless communication system

ABSTRACT

A method of transmitting uplink data is provided. The method includes establishing connections with a first serving cell and a second serving cell, determining, by a user equipment (UE), a time period for a device-to-device (D2D) discovery signal communication via the second serving cell, determining, by the UE and based on an uplink grant received via the first serving cell, a first subframe associated with an uplink signal to an evolved NodeB (eNB) associated with the first serving cell, and in response to determining that the first subframe overlaps in time with the time period, refraining from transmitting the uplink signal in the first subframe, and transmitting, based on a retransmission timing, the uplink signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/427,460, filed on Feb. 8, 2017, which is a continuation of PCTInternational Patent Application No. PCT/KR2015/008295, filed on Aug. 7,2015, which claims priority from and the benefit of Korean PatentApplication Nos. 10-2014-0102644, filed on Aug. 8, 2014,10-2014-0102678, filed on Aug. 9, 2014, and 10-2014-0103988, filed onAug. 11, 2014, each of which is hereby incorporated by reference in itsentirety.

BACKGROUND 1. Field

The present disclosure relates to wireless communication, and moreparticularly, to a method and apparatus for transmitting uplink dataduring a user equipment's monitoring period for receiving a particularsignal in a wireless communication system.

2. Discussion of the Background

Device to device (D2D) communication is a communication scheme that hasbeen utilized from the advent of the analog radio set. However, D2Dcommunication in a wireless communication system is distinguished fromexisting D2D communication schemes.

D2D communication in a wireless communication system indicatescommunication in which geographically close user equipments (UEs) usethe transmission/reception technologies of the wireless communicationsystem in- or outside of the frequency band of the wirelesscommunication system, and directly transmit and receive data between theUEs without sending data through infrastructure such as a base station(BS). This enables a UE to utilize wireless communication outside anarea where wireless communication infrastructure is established, andreduces the network load of the wireless communication system.

A UE that supports D2D communication in the wireless communicationsystem may also perform general wireless communication (that is,communication with a serving BS using a cell (carrier) provided by theserving BS). To this end, the serving BS transmits an uplink grantindicating transmission of a Physical Uplink Shared Channel (PUSCH) to aUE in the cell. The PUSCH carries an Uplink Shared Channel (UL-SCH), anduplink data (i.e., data to be transmitted to the BS) is transmittedthrough the UL-SCH.

However, a UE (D2D UE) that supports D2D communication needs to monitorwhether a D2D signal is received from another D2D UE for D2Dcommunication. Therefore, when the uplink grant received from the BSindicates transmission of a PUSCH during a period for monitoring a D2Dsignal, a UE that has a single transceiver chain (that is, a UEincapable of performing transmission and reception in parallel) may notperform either a PUSCH transmission or a D2D signal monitoring. Inaddition, even when a D2D UE is capable of performing transmission andreception in parallel, self-interference may occur, in which atransmission signal of the D2D UE is received by the D2D UE, when aPUSCH is transmitted during a D2D signal monitoring period.

To overcome the above described drawback, D2D communication needs amethod for effectively performing a D2D signal transmission andreception by minimizing the effect on an existing LTE signal.

The D2D communication may be performed using a communication scheme thatuses a non-licensed band such as Bluetooth or a wireless LAN. However, acommunication scheme that uses the non-licensed band will havedifficulty providing a planned and controlled service, which is adrawback. Particularly, the performance may be dramatically reduced byinterference. Conversely, device-to-device direct communication may beoperated or provided in a licensed band or in an environment whereinter-system interference is under control, and may therefore be capableof supporting quality of service (QoS), of raising frequency utilizationefficiency through frequency reuse, and of increasingcommunication-enabled distance.

In D2D communication in a licensed band, that is, a cellularcommunication-based D2D communication, a resource for D2D communicationmay be allocated through a BS and a cellular uplink spectrum.Alternately, uplink subframes may be used as the allocated resources.

The D2D discovery and communication may be operated independently fromthe cellular communication. In some instances, a Wide Area Network (WAN)signal is transmitted to a D2D UE from a BS through a DL spectrum and,at the same time, a D2D signal may be transmitted from another UE. Inthis instance, a UE having a single transceiver chain may be incapableof simultaneously transmitting or receiving signals through manyfrequency bands, which is a drawback. Therefore, the priority of signalsto be processed must be determined and the handling of remaininglow-priority signals must be defined.

SUMMARY

An aspect of the present disclosure is to provide a method and apparatusfor transmitting uplink data in a wireless communication system thatsupports device to device (D2D) communication.

Another aspect of the present disclosure is to provide a method andapparatus for minimizing the effect of D2D communication on a wirelesscommunication system that supports D2D communication when D2Dcommunication is performed in the wireless communication system.

Another aspect of the present disclosure is to provide a wirelesscommunication method and apparatus in association with a D2D signal.

Another aspect of the present disclosure is to provide a method andapparatus for preventing a collision between a D2D signal and a WANsignal.

Another aspect of the present disclosure is to provide a method andapparatus for determining priority of signals when a D2D signal and aWAN signal collide.

Another aspect of the present disclosure is to provide a method andapparatus for determining a procedure for processing a signal having alower priority when a D2D signal and a WAN signal collide.

Another aspect of the present disclosure is to provide a method andapparatus for defining a procedure for processing a Physical HARQIndicator Channel (PHICH) when a D2D signal reception and a PHICHreception occur at the same time.

Another aspect of the present disclosure is to provide a method andapparatus for defining a UL HARQ operation when a D2D monitoring periodand a PHICH reception timing overlap.

An exemplary embodiment provides a method of transmitting uplink data,the method including: establishing connections with a first serving celland a second serving cell; determining, by a user equipment (UE), a timeperiod for a device-to-device (D2D) discovery signal communication viathe second serving cell; determining, by the UE and based on an uplinkgrant received via the first serving cell, a first subframe associatedwith an uplink signal to an evolved NodeB (eNB) associated with thefirst serving cell; and in response to determining that the firstsubframe overlaps in time with the time period, refraining fromtransmitting the uplink signal in the first subframe, and transmitting,based on a retransmission timing, the uplink signal.

An exemplary embodiment provides a method of transmitting uplink data,the method including: determining, by a user equipment (UE), a timeperiod for monitoring a device-to-device (D2D) discovery signalcommunication; determining, by the UE, a first subframe associated witha Hybrid Automatic Repeat Request (HARQ) feedback reception; and basedon whether the first subframe overlaps in time with the time period,setting a state variable associated with the HARQ feedback reception toacknowledgement.

An exemplary embodiment provides a user equipment to transmit uplinkdata, the UE including: a transmitter; a memory; and a processor. Theprocessor may establish connections with a first serving cell and asecond serving cell, determine a time period for a device-to-device(D2D) discovery signal communication via the second serving cell,determine, based on an uplink grant received via the first serving cell,a first subframe associated with an uplink signal to an evolved NodeB(eNB) associated with the first serving cell, and in response todetermining that the first subframe overlap in time with the timeperiod, control the transmitter to refrain from transmitting the uplinksignal in the first subframe, and control the transmitter to transmit,based on a retransmission timing, the uplink signal.

According to the present disclosure, the effect of D2D communication ona wireless communication system may be minimized when the D2Dcommunication is performed in the wireless communication system, and auser equipment (UE) may flexibly perform both an uplink transmission andD2D communication.

According to the present disclosure, general operations of a UE and a BSmay be defined according to priority when a D2D signal and a WAN signalcollide, and the effect of the D2D signal on WAN performance may beminimized when a UE performs D2D communication.

According to the present disclosure, from the perspective of a UE, D2Ddiscovery and D2D communication may be supported through limited UEcapabilities (e.g., a single transceiver chain based-UE), and the WANperformance may be corrected by providing a method of receiving andprocessing various physical channels (e.g., a PHICH) that carry a signalreceived over a WAN.

According to the present disclosure, by effectively controlling a PHICHreception in a D2D environment, an uplink (UL) HARQ operation may beefficiently implemented and unnecessary consumption of radio resourcesin a network may be reduced.

A UE may transmit or receive a D2D signal according to priority, and maygenerally secure efficiency of D2D discovery and D2D communication.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a wireless communication systemaccording to the present disclosure.

FIG. 2 is a diagram illustrating the concept of cellular network-basedD2D communication according to the present disclosure.

FIG. 3 is a flowchart illustrating a PUSCH transmission method accordingto an embodiment of the present disclosure.

FIG. 4 is a diagram illustrating operations executed when a PUSCHtransmission on a measurement gap is indicated in an LTE system.

FIGS. 5 and 6 are diagrams illustrating the case of performing anon-adaptive retransmission according to an embodiment of the presentdisclosure.

FIG. 7 is a flowchart illustrating the operations of a base station (BS)according to an embodiment of the present disclosure.

FIG. 8 is a block diagram illustrating a wireless communication systemaccording to an embodiment of the present disclosure.

FIGS. 9 and 10 are diagrams illustrating the case in which an initialPUSCH transmission and an SRS transmission are performed in a monitoringperiod according to an embodiment of the present disclosure.

FIG. 11 is a flowchart illustrating the operations of a BS and a D2Dreception UE according to an embodiment of the present disclosure.

FIG. 12 is a block diagram illustrating a wireless communication systemaccording to an embodiment of the present disclosure.

FIG. 13 is a diagram illustrating the structure of an MAC entity of aUE.

FIG. 14 is a diagram illustrating the concept of cellular network-basedD2D communication according to the present disclosure.

FIG. 15 is a diagram illustrating an example of a DL subframe in which aUE is incapable of receiving a PHICH.

FIG. 16 is a diagram illustrating an example of a measurement gap in aWAN system.

FIG. 17 is a diagram illustrating a UL HARQ operation according to anembodiment of the present disclosure.

FIG. 18 is a diagram illustrating a UL HARQ operation according toanother embodiment of the present disclosure.

FIGS. 19 and 20 are diagrams illustrating UL HARQ operations in a systemin which carrier aggregation is configured.

FIG. 21 is a flowchart illustrating a UL HARQ performing method when aD2D monitoring period and a PHICH reception timing overlap.

FIG. 22 is a flowchart illustrating the operations of a UE according tothe present disclosure.

FIG. 23 is a block diagram illustrating an example of another UEaccording to the present disclosure.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Hereinafter, a few embodiments of the present disclosure will bedescribed with reference to the exemplary drawings. In the followingdescription, the same elements will be designated by the same referencenumerals although they are shown in different drawings. Further, in thefollowing description of the present disclosure, a detailed descriptionof known functions and configurations incorporated herein will beomitted when the description may make the subject matter of the presentdisclosure unclear.

In addition, the present specification provides descriptions associatedwith a wireless communication network. Tasks executed in the wirelesscommunication network may be performed in a process where a system (forexample, a base station) that manages the corresponding wirelesscommunication network controls a network and transmits data, or may beperformed in a terminal included in the corresponding wireless network.

FIG. 1 is a diagram illustrating a wireless communication systemaccording to the present disclosure.

Referring to FIG. 1, a wireless communication system 10 may provide acommunication service between a base station (BS) and a user equipment(UE). In a wireless communication system, a UE and a BS may wirelesslytransmit and receive data. Also, the wireless communication system maysupport Device-to-Device (D2D) communication between UEs. The wirelesscommunication system that supports the D2D communication will bedescribed later.

A BS 11 of the wireless communication system 10 may provide acommunication service to a UE that exists within the transmissioncoverage area of the BS 11, through a predetermined frequency band. Thecoverage area serviced by a BS may be also referred to as a site. Thesite may include various areas 15 a, 15 b, and 15 c, which may bereferred to as sectors. The sectors included in the site may bedistinguished from each other based on different identifiers. Eachsector 15 a, 15 b, and 15 c may be construed as a part of the area thatthe BS 11 covers.

The BS 11 indicates a station that communicates with the UE 12, and maybe referred to by terms such as an evolved-NodeB (eNodeB or eNB), a basetransceiver system (BTS), an access point, a femto eNodeB, a Home eNodeB(HeNodeB), a relay, a remote radio head (RRH), or the like.

The UE 12 may be a stationary or mobile entity, and may be referred toby terms such as a mobile station (MS), an advanced MS (AMS), a userterminal (UT), a subscriber station (SS), a wireless device, a personaldigital assistant (PDA), a wireless modem, a handheld device, or thelike.

The BS 11 may be referred to as a mega cell, a macro cell, a micro cell,a pico cell, a femto cell, or the like according to the size of coverageprovided by the corresponding BS. A cell may be used as a term forindicating a frequency band that a BS provides, a site of a BS, or a BS.

Hereinafter, a downlink indicates communication or a communication pathfrom the BS 11 to the UE 12, and an uplink indicates communication or acommunication path from the UE 12 to the BS 11. In a downlink, atransmitter may be a part of the BS 11, and a receiver may be a part ofthe UE 12. In an uplink, a transmitter may be a part of the UE 12 and areceiver may be a part of the BS 11.

A multiple access scheme applied to a wireless communication systemmight not be limited. For example, the wireless communication system mayutilize various multiple access schemes, such as Code Division MultipleAccess (CDMA), Time Division Multiple Access (TDMA), Frequency DivisionMultiple Access (FDMA), Orthogonal Frequency Division Multiple Access(OFDMA), Single Carrier-FDMA (SC-FDMA), OFDM-FDMA, OFDM-TDMA, OFDM-CDMA,or the like. Further, modulation schemes may modulate signals receivedfrom multiple users of a communication system, thereby increasing thecapacity of the communication system. Also, an uplink transmission and adownlink transmission may be performed based on a time division duplex(TDD) scheme that performs transmission based on different times, orbased on a frequency division duplex (FDD) scheme that performstransmission based on different frequencies.

The layers of a radio interface protocol between a UE and a BS may beclassified as a first layer (L1), a second layer (L2), and a third layer(L3), based on the three low layers of an Open System interconnection(OSI) model.

A physical layer belonging to a L1 provides an information transferservice using a physical channel. A physical layer is connected to ahigher Media Access Control (MAC) layer through a transport cannel. Atransport channel transfers data between the MAC layer and the physicallayer. The transport channel is classified based on a scheme oftransmitting data through a radio interface. In addition, a physicalchannel transfers data between different physical layers (that is,between physical layers of a UE and a BS). A physical channel may bemodulated based on an Orthogonal Frequency Division Multiplexing (OFDM)scheme, and uses space formed of time and frequencies and a plurality ofantennas as radio resources.

For example, a Physical Downlink Control CHannel (PDCCH) among physicalchannels may inform a UE of the resource allocation for a Paging CHannel(PCH) and a DownLink Shared CHannel (DL-SCH). Further, a PDCCH mayinform a UE of Hybrid Automatic Repeat Request (HARQ) informationassociated with a DL-SCH, and may deliver to a UE an uplink schedulinggrant which reports resource allocation of an uplink transmission. APhysical Control Format Indicator CHannel (PCFICH) informs a UE of thenumber of OFDM symbols used for PDCCHs, and is transmitted for eachsubframe. A Physical Hybrid ARQ Indicator CHannel (PHICH) carries a HARQACK/NACK signal in response to an uplink transmission. In addition, aPhysical Uplink Control CHannel (PUCCH) delivers HARQ ACK/NACK withrespect to a downlink transmission and uplink control information suchas scheduling request, a Channel Quality Indicator (CQI), a rankindicator (RI), or the like.

The RI is information associated with the rank (that is, the number oflayers) that a UE recommends. That is, the RI indicates the number ofindependent streams used for spatial multiplexing. The RI is fed backonly when a UE operates in an MIMO mode that uses spatial multiplexing.The RI is related to one or more CQI feedbacks. That is, a fed back CQImay be calculated by assuming a predetermined RI value. Generally, therank of a channel varies more slowly than a CQI and thus, the number oftimes that an RI is fed back is smaller than that of the CQI. Thetransmission period of an RI may be a multiple of the transmissionperiod of a CQI/PMI. The RI is given for an overall system band, andselective RI feedback based on a frequency may not be supported.

A Physical Uplink Shared CHannel (PUSCH) delivers an UpLink SharedCHannel (UL-SCH). The PUSCH may include Channel State Information (CSI),such as a CQI, and HARQ ACK/NACK by request or according to aconfiguration made by a BS.

A data link layer corresponding to the second layer of the OSI model mayinclude a MAC layer, a Radio Link Control (RLC) layer, and a Packet DataConvergence Protocol (PDCP) layer.

The MAC layer may execute mapping between a logical channel and atransport channel, and execute multiplexing or demultiplexing of a MACService Data Unit (SDU) that belongs to the logical channel to transportblocks provided to a physical channel on a transport channel. The MAClayer may provide a service to an RLC layer through a logical channel.The logical channel may be divided as a control channel for transferringcontrol plane information and a traffic channel for transferring userplane information. For example, services provided from the MAC layer toa higher layer may include a data transfer service or a radio resourceallocation service.

The RLC layer may perform concatenation, segmentation, and reassembly ofan RLC SDU. The RLC layer provides three types of operation modes, suchas a Transparent Mode (TM), an Unacknowledged Mode (UM), and anAcknowledged Mode (AM), to secure various quality of services (QoS)required by a Radio Bearer (RB).

A PDCP layer may perform (a) user data delivery, (b) header compressionand ciphering, and (c) control plane data delivery andciphering/integrity protection.

Referring to FIG. 3, an RRC layer controls a logical channel, atransport channel, and a physical channel, in association withconfiguration, reconfiguration, and release of RBs. An RB indicates alogical path provided by a first layer (PHY layer) and a second layer(MAC layer, RLC layer, and PDCP layer) for transferring data between aUE and a network. The process of configuring an RB defines properties ofa radio protocol layer and a channel for providing a predeterminedservice; the configuration also sets corresponding detailed parametersand an operation method. An RB may be classified as a Signaling RB (SRB)or a Data RB (DRB). An SRB is used as a path for transmitting an RRCmessage and a Non-Access Stratum (NAS) message in the control plane, anda DRB is used as a path for transmitting user data in the user plane.Hereinafter, the term “RB” that is expressed without distinguishingbetween an SRB and a DRB indicates a DRB.

FIG. 2 is a diagram illustrating the concept of cellular network-basedD2D communication according to the present disclosure.

D2D communication refers to a technology in which UEs directly receiveand transmit data. Hereinafter, a UE disclosed in embodiments of thepresent disclosure is assumed to support D2D communication. Also, D2Dmay be interchangeably used with a Proximity-based Service (ProSe) orProSe-D2D. The use of the term “ProSe” for D2D does not indicate thatthe meaning of a technology which directly transmits/receives databetween UEs is changed, but instead that a proximity-based service maybe added.

Recently, research has been conducted on a method of performingdiscovery and direct communication between devices in- or outside ofnetwork coverage (in-coverage devices or out-of-coverage devices) forpurpose of public safety or the like. A UE that transmits a signal basedon the D2D communication is defined as a transmission UE (Tx UE), and aUE that receives a signal based on the D2D communication is defined as areception UE (Rx UE). The Tx UE may transmit a discovery signal and theRx UE may receive a discovery signal. The Tx UE and the Rx UE mayoperate by exchanging their roles. A signal transmitted by the Tx UE maybe received by two or more Rx UEs.

When UEs located close to one another execute D2D communication in acellular system, loads on a BS may be dispersed. In addition, when UEsexecute D2D communication, a UE transmits data a relatively shortdistance, and thus, transmission power consumption and transmissionlatency of a UE may decrease. In addition, from the perspective of anoverall system, existing cellular-based communication and D2Dcommunication use the same resources and thus the frequency usageefficiency may potentially be improved. However, interference betweencellular-based and D2D communication needs to be considered and thuseach communication basically performs transmission on differentsubframes.

D2D communication may be classified as a communication method for a UElocated within a network coverage area (base station coverage) and acommunication method of a UE located outside a network coverage area(base station coverage).

Referring to FIG. 2, communication between a first UE 210 located in afirst cell and a second UE 220 located in a second cell andcommunication between a third UE 230 located in the first cell and afourth UE 240 located in a first cluster may be D2D communication in anetwork coverage area. The communication between the fourth UE 240located in the first cluster and a fifth UE 250 located in the firstcluster may be D2D communication between the UEs located outside anetwork coverage area. Here, the fifth UE 250 may operate as the ClusterHead (CH) of a first cluster. A CH is a UE (or unit) used as a referencefor at least the purpose of synchronization, and occasionally indicatesa UE that allocates a resource for different purposes. The CH mayinclude an Independent Synchronization Source (ISS) for thesynchronization of out-of-coverage UEs.

D2D communication may include a discovery process that executesdiscovery for communication between UEs and may include a directcommunication process in which UEs transmit and receive control dataand/or traffic data. D2D communication within a network coverage areamay be used for purposes including public safety, an ultra-low latencyservice, commercial services, or the like. D2D communication outside anetwork coverage area may be used for only public safety.

As an embodiment in association with executing D2D communication, a BS200 may transmit D2D resource allocation information to the first UE210. The first UE 210 is a UE located within the coverage area of the BS200. The D2D resource allocation information may include allocationinformation associated with a transmission resource and/or receptionresource that may be used for D2D communication between the first UE 210and another UE (e.g., a second UE 220).

The first UE 210 that receives the D2D resource allocation informationfrom the BS may transmit the D2D resource allocation information to thesecond UE 220. The second UE 220 may be a UE located outside thecoverage area of the BS 200. The first UE 210 and the second UE 220 mayexecute D2D communication based on the D2D resource allocationinformation. Particularly, the second UE 220 may obtain informationassociated with the D2D communication resources of the first UE 210. Thesecond UE 220 may receive data transmitted from the first UE 210,through a resource indicated by the information associated with the D2Dcommunication resources of the first UE 210.

In the D2D communication, a UE may transmit physical layer control datato another UE. Here, in D2D communication, physical layer control datafor synchronization may be transmitted through a synchronizationchannel, for example, a Physical D2D Synchronization Channel (PD2DSCH).Physical layer control data for data communication may be transmittedthrough scheduling assignment (SA), and may be provided in a form thatis similar to a PUSCH format for D2D communication or in a slightlyimproved variant of the PUSCH format. In D2D communication, traffic datathat is practical data, distinguished from physical layer control data,may be expressed as D2D data.

Furthermore, a method of transmitting higher layer control data inaddition to a physical layer in D2D communication may be defined.

When D2D communication is performed, a UE may operate in a firsttransmission mode or in a second transmission mode. The firsttransmission mode is a mode in which a UE performs D2D communicationonly when the UE is assigned with a resource for D2D communication froma BS. The BS transmits a D2D grant to a Tx UE for purpose of D2Dresource allocation. The D2D grant indicates, for a Tx UE, parameterinformation that the BS needs to determine using Scheduling Assignment(SA) information, which is control information that an Rx UE needs toobtain for D2D data reception when D2D communication is performed. Theparameter information may include, for example, resource allocation(Resource Pattern for Transmission (RPT))/power control/TA informationand the like in association with the SA, and Resource Allocation forTransmission (RPT)/power control/TA information and the like inassociation with data indicated by the SA. The parameter informationthat the BS needs to determine may include resource allocationinformation associated with data indicated by the SA, and the like. TheD2D grant may be transferred to a Tx UE through an (E)PDCCH channelincluding Downlink Control Information (DCI). The D2D grant is controlinformation identified as information to be used for D2D throughD2D-Radio Network Temporary Identifier (D2D-RNTI) allocated for each UE,differed from an uplink grant. The D2D grant may be also referred to asa SA/data grant.

The second transmission mode is a mode in which a UE performs D2Dcommunication in an environment (out-of-coverage) that does not haveindication by a BS or an environment (in-coverage) that uses only arestrictive indication. The UE may autonomously and randomly select aresource to be used from among available radio resources for D2Dcommunication, and transmits D2D data. When information indicates that apredetermined cell in the BS is capable of supporting D2D through asystem information block (SIB) dedicated signaling and when D2D resourcepool information for the second mode provided from the BS exist, the UEmay operate in the second transmission mode only in the predeterminedcell. When the information indicating that a predetermined cell in theBS is capable of supporting D2D but the D2D resource pool informationfor the second transmission mode is not provided, the UE switches to anRRC-connected mode to operate in the second transmission mode, andperforms the second transmission mode through dedicated RRC signaling.When the UE is located outside the network service area (that is, whenthe UE is an RRC idle mode UE but is also in an “Any Cell Selection”mode, which indicates that the UE does not select a service-enabledcell), the UE may operate in the second transmission mode using D2Dresource pool information for the second transmission mode stored in aUniversal Subscriber identity Module (USIM) Integrated Circuit Card(UICC) of the UE or the like, or D2D resource pool information for thesecond transmission mode that is received a BS in a previous networkservice area.

In the wireless communication system, a UE reports its buffer state to aBS to receive an allocation of a resource, which is required fortransmitting uplink data (data to be transferred to the BS) in thebuffer in the UE. Then the BS schedules resources to be allocated toeach UE based on information associated with the buffer state receivedfrom a UE.

Therefore, when the wireless communication system supports D2Dcommunication, the BS may need to schedule the resources required whenany UEs existing in the coverage area (in-coverage UEs) transmit databased on mode 1 D2D communication. To this end, the BS needs to be awareof the amount of data to be transmitted in D2D communication(hereinafter D2D data), which is included in the buffer of a UE. To thisend, through the following procedures, the UE reports, to the BS, theamount of data to be transmitted in D2D communication, which is includedin the buffer of the UE.

A UE (D2D UE) that supports D2D communication in the wirelesscommunication system may also perform wireless communication (e.g., LTEcommunication) using a BS. The wireless communication using a BS refersto communication in which a UE performs communication with a serving BSusing a cell (carrier) provided by the serving BS. To this end, theserving BS transmits an uplink grant indicating a Physical Uplink SharedChannel (PUSCH) transmission to a UE in the cell. The PUSCH carries anUplink Shared Channel (UL-SCH). Uplink data may be transmitted to a BSthrough the UL-SCH.

However, the D2D UE needs to monitor whether a D2D signal is receivedfrom another D2D UE for D2D communication. Therefore, when the uplinkgrant received from the BS indicates transmission of a PUSCH during aperiod for monitoring a D2D signal, a UE that has a single transceiverchain (that is, a UE incapable of performing transmission and receptionin parallel) may not perform either PUSCH transmission or D2D signalmonitoring. In addition, although the D2D UE is capable of performingtransmission and reception in parallel, self-interference may occur, inwhich a D2D UE transmission signal is received by the D2D UE when aPUSCH is transmitted during a D2D signal monitoring period. Therefore,hereinafter, a method of transmitting a PUSCH without the abovedescribed drawback will be described.

FIG. 3 is a flowchart illustrating a PUSCH transmitting method accordingto an embodiment of the present disclosure. FIG. 4 is a diagramillustrating operations performed when a PUSCH transmission on ameasurement gap configured on a DL spectrum/subframe is indicated. FIGS.5 and 6 are diagrams illustrating the case of performing a non-adaptiveretransmission according to an embodiment of the present disclosure.

Referring to FIG. 3, a D2D UE receives D2D configuration information forD2D communication from a BS in operation S310. The D2D communicationincludes D2D discovery and D2D data communication as a matter of course.The D2D configuration information may be transmitted to D2D UEs througha System Information Block (SIB) and/or a dedicated RRC signal accordingto a D2D discovery type (type 1/2B) or a D2D data communication mode(mode 1/2). For example, when a UE is set to a first transmission mode,the UE may perform D2D communication using resources allocated from aBS. When a UE is set to a second transmission mode, the UE may performD2D communication using resources that the UE may autonomously selectfrom the D2D resource pool.

The information associated with the D2D resource pool may includeinformation associated with a D2D signal monitoring period (monitoringresource information). The monitoring period is a time period set by aserving BS to enable a UE to receive a D2D signal existing on otherresources (e.g., carrier) that the UE currently does not monitor, or themonitoring period may be a time period that the UE autonomouslyrecognizes based on information obtained through an initial accessoperation on other resources (e.g., carrier/PLMN). The monitoringresource information may exist in a form identical to the informationassociated with the D2D resource pool or a subset thereof. For example,the monitoring resource information may include information associatedwith a period (e.g., a subframe) for monitoring D2D signals (e.g., adiscovery signal) of any D2D UEs that access a Public Land MobileNetwork (PLMN) that provides a serving cell to UEs. Here, the PLMNindicates a mobile communication network operator network or anidentification number of a corresponding network. A network may identifya network operator that operates a corresponding frequency for a UEbased on an identifier of the corresponding network, and may obtaininformation associated with an access privilege (e.g., access classbarring).

Alternatively, the monitoring resource information may includeinformation associated with a period for monitoring D2D signals of D2DUEs, which access a PLMN (serving PLMN) that provides a serving cell toa UE, and information associated with a period for monitoring D2Dsignals of D2D UEs, which access a neighboring or different PLMN. Toeffectively monitor both D2D signals of D2D UEs that access differentcells (inter-cell) and D2D signals of D2D UEs that access differentPLMNs (inter-PLMN), a predetermined monitoring period may need to beconfigured for a D2D UE. As described above, when a monitoring period isconfigured/obtained with respect to a neighboring or different PLMN, aD2D signal from a different PLMN (carrier) or a neighboring cell needsto be monitored only in the corresponding monitoring period. Therefore,D2D signal reception efficiency may increase and the amount of batteryconsumption may decrease.

The UE receives an uplink grant indicating transmission of a PUSCH or aPUSCH and SRS from the BS in operation S320. The uplink grant may bereceived before a transmission mode for D2D data communication (firsttransmission mode or second transmission mode) or a transmission typefor D2D discovery (type 1 and type 2B) is set for the UE, or the uplinkgrant may be received after the D2D transmission mode/discovery type isset. When the uplink grant is received after a D2D transmission mode isset for the UE through the D2D configuration information, the UEdetermines whether transmission timing for a PUSCH or a PUSCH and SRS,indicated by the uplink grant, is included in a monitoring period forD2D communication in operation S330.

When the uplink grant indicates transmission of a PUSCH or a PUSCH andSRS within the monitoring period for D2D communication, the UE mayprocess the uplink grant but may not perform (may keep) transmission ofthe PUSCH or the PUSCH and SRS to the BS in order to receive a D2Dsignal. Subsequently, the UE performs transmission at a subsequent PUSCHor PUSCH and SRS retransmission timing according to a non-adaptiveretransmission procedure in operation S340. Here, the non-adaptiveretransmission procedure refers to the retransmission of a PUSCH or aPUSCH and SRS at a subsequent PUSCH transmission opportunity without aHARQ ACK/NACK from a BS, as a response (feedback) to an uplinktransmission associated with an indicated timing for the transmission ofa PUSCH or a PUSCH and SRS. To this end, when the uplink grant indicatestransmission of a PUSCH or a PUSCH and SRS within a monitoring periodfor D2D communication, the UE may store the uplink grant received from aHARQ entity but may not indicate corresponding transmission for aphysical layer. However, when the uplink grant indicates transmission ofa PUSCH beyond the monitoring period, the UE transmits a PUSCH (or aPUSCH and SRS) at an indicated timing in operation S350.

That is, as the case in which a UE having a single transceiver chainreceives an indication of transmission of a PUSCH or PUSCH and SRS on ameasurement gap as illustrated in FIG. 4, when a D2D UE receives anindication of transmission of a PUSCH or a PUSCH and SRS within amonitoring period for D2D communication, the D2D UE may transmit a PUSCHand a PUSCH and SRS at a subsequent PUSCH or PUSCH and SRSretransmission timing without HARQ feedback. Here, the measurement gapindicates a period for determining and measuring cells corresponding toremaining frequencies (inter-frequency and/or inter-Radio AccessTechnology (RAT)), excluding the carrier frequency of a serving cell.The measurement gap may be classified as a first gap pattern that isrepeated based on a period of 40 ms and has a length of 6 ms, and as asecond gap pattern that is repeated based on a period of 80 ms and has alength of 6 ms. A network may configure one of the two patterns for aUE.

TABLE 1 Minimum available time for Measurement inter-frequency and Gapinter-RAT MeasurementGap Repetition measurements Gap Length (MGL,Period(MGRP, during 480 ms Measurement Pattern Id ms) ms)period(Tinter1, ms) Purpose 0 6 40 60 Inter-Frequency E-UTRAN FDD andTDD, UTRAN FDD, GERAN, LCR TDD, HRPD, CDMA2000 1x 1 6 80 30Inter-Frequency E-UTRAN FDD and TDD, UTRAN FDD, GERAN, LCR TDD, HRPD,CDMA2000 1x

A trade-off exists between the first pattern and the second pattern. Thefirst pattern has a short period but the transmission/reception of aserving cell is disturbed by interference. Conversely, the secondpattern has a longer period, but less disturbs thetransmission/reception of the serving cell. A UE may be incapable oftransmitting any data to a BS during a measurement gap.

FIG. 4 illustrates the case in which a measurement gap is configuredfrom an n+2^(th) subframe to an n+7^(th) subframe for a UE, and in whichthe UE receives an uplink grant indicating an initial PUSCH transmissionin an n+4^(th) subframe from a BS in an n^(th) subframe. In thisinstance, the UE does not transmit a PUSCH in the n+4^(th) subframe, andinstead transmits the PUSCH at a subsequent retransmission timing (thatis, an n+12^(th) subframe). In this instance, the UE may not receiveHARQ feedback at an n+8^(th) subframe from the BS.

Referring to FIG. 5, in the case in which subframes from an n+3^(th)subframe to an n+6^(th) subframe are configured for a UE that isprovided with a first carrier from a first base station (eNB1) belongingto a serving PLMN, as a monitoring period with respect to a D2D signal(e.g., a discovery signal for D2D discovery) of a D2D UE that accesses aneighboring PLMN, when the UE receives an uplink grant indicating aninitial PUSCH transmission in n+4^(th) subframe from the first BS in then^(th) subframe of the first carrier, the UE may process the uplinkgrant but may not transmit a PUSCH in the n+4^(th) subframe of the firstcarrier in order to receive a D2D signal. Subsequently, the UE maytransmit the PUSCH, which has not been transmitted, at a subsequentretransmission timing (that is, the n+12^(th) subframe) without HARQfeedback, through the non-adaptive retransmission. That is, when thereis a possibility that a D2D signal reception based on a monitoringperiod and a PUSCH transmission based on an uplink grant occur at thesame time, performing the D2D signal reception and the PUSCHtransmission at the same time is not allowed in order to avoidself-interference. Therefore, the UE might not perform any uplinktransmission on a resource that is configured for monitoring resourceinformation for reception of a D2D signal, and the UE may transmit aPUSCH at a subsequent retransmission timing without a HARQ-ACK/NACKreception from the BS (non-adaptive retransmission). The non-adaptiveretransmission may include a transmission performed at the same powerand the MCS level, which have been used for a previous Physical UplinkShared Channel (PUSCH) transmission.

FIG. 5 illustrates transmission of a PUSCH at a retransmission timingwhen an indication that indicates a PUSCH transmission in a monitoringperiod for monitoring D2Ds signals of D2D UEs that access differentPLMNs (inter-PLMN) is received. However, it is equally applied to thecase in which an indication that indicates a PUSCH transmission in amonitoring period for D2D signals of D2D UEs that access different cells(inter-cell) provided by a single network operator is received.

FIG. 6 illustrates the case in which different cells (carriers) providedby a single network operator are asynchronous. A period for monitoringD2D signals of D2D UEs that access a neighboring cell (from an n+3^(th)subframe to an n+6^(th) subframe) and a timing for PUSCH transmissionindicated by the uplink grant (an n+4^(th) subframe) are not identical;they partially overlap. However, though the UE processes the uplinkgrant, it may not transmit a PUSCH at the indicated n+4^(th) subframe inthe same manner as the above description. Subsequently, the UE maytransmit the PUSCH, which has not been transmitted, at a subsequentretransmission timing (that is, an n+12^(th) subframe) without HARQfeedback through the non-adaptive retransmission. When the n+12^(th)subframe and a period for monitoring D2D signals of D2D UEs that accessanother neighboring cell overlap again, the UE may transmit the PUSCH atan n+20^(th) subframe (not illustrated).

FIG. 7 is a flowchart illustrating the operations of a BS according toan embodiment of the present disclosure.

Referring to FIG. 7, a BS transmits D2D configuration information to aUE in a cell in operation S710. The D2D configuration information may betransmitted to the UE for D2D discovery or for D2D data transmissionthrough, for example, a System Information Block (SIB) or a dedicatedRRC signal. The information associated with the D2D resource pool mayinclude information associated with a D2D signal monitoring period(monitoring resource information).

For example, the monitoring resource information may include informationassociated with a period for monitoring D2D signals of D2D UEs thataccess a single operator's network. Alternatively, the monitoringresource information may include both information associated with aperiod for monitoring D2D signals of D2D UEs that access the singleoperator's network and information associated with a period formonitoring D2D signals of D2D UEs that access a different operator'snetwork.

The BS transmits an uplink grant indicating transmission of a PUSCH tothe UE in operation S720. The UE that receives the uplink granttransmits a PUSCH using timing indicated by the uplink grant or at aretransmission timing based on monitoring information (informationassociated with a resource monitored by the UE for D2D communication) bychecking whether a D2D signal reception and an uplink PUSCH transmissioncollide, and the BS processes the PUSCH received from the UE inoperation S730. In this instance, the BS may not transmit a HARQACK/NACK even though the PUSCH is not received at the timing for a PUSCHtransmission that the BS indicates through the uplink grant.

FIG. 8 is a block diagram illustrating a wireless communication systemaccording to an embodiment of the present disclosure.

Referring to FIG. 8, a wireless communication system that supports D2Dcommunication may include a UE 800 and a BS (or cluster head) 850.

The UE 800 includes a processor 805, a Radio Frequency (RF) unit 810,and a memory 815. The memory 815 is connected with the processor 805,and stores various pieces of information for driving the processor 805.The RF unit 810 is connected with the processor 805, and transmitsand/or receives a radio signal. For example, the RF unit 810 mayreceive, from the BS 850, D2D configuration information which isdisclosed in the present specifications, and an uplink indicating aPUSCH transmission. Also, the RF unit 810 may transmit a PUSCH to the BS850 using timing indicated by the uplink grant or a retransmissiontiming.

The memory 815 may store D2D configuration information, resource poolinformation for the second transmission mode, and information associatedwith a monitoring period for reception of a D2D signal, and may thenprovide the information to the processor 805 upon request of theprocessor 805.

The processor 805 may implement functions, processes, and/or methodsproposed in the present specification. Particularly, the processor 805may implement all of the operations of FIG. 3. For example, theprocessor 805 may include a monitoring unit 806, a PUSCH configuringunit 807, and a transmission timing determining unit 808.

The monitoring unit 806 may monitor a D2D signal during a monitoringperiod configured based on information associated with the monitoringperiod for reception of a D2D signal. The monitoring unit 806 determineswhether an uplink grant indicating a PUSCH transmission in themonitoring period is received. Here, the information associated with themonitoring period may be transmitted to the UE 800 through an SIB and/ora dedicated RRC signal.

When it is determined that the uplink grant indicating a PUSCHtransmission in the monitoring period is received, the PUSCH configuringunit 807 processes the uplink grant and configures a PUSCH.

The transmission timing determining unit 808 determines a timing inwhich to transmit the PUSCH configured by the PUSCH configuring unit 807according to whether the uplink grant indicating a PUSCH transmission inthe monitoring period is received. For example, when the uplink grantindicating a PUSCH transmission in the monitoring period is received,the transmission timing determining unit 808 determines to transmit theconfigured PUSCH at a retransmission timing. The retransmission timingof the PUSCH is a value that varies based on the TDD/FDD mode of aserving cell that transmits the PUSCH. For example, in the FDD mode,retransmission may be performed after subframes corresponding to 8 ms.In the TDD mode, retransmission may be performed after a subframe valuedistinguished based on a set UL/DL configuration. Conversely, when theuplink grant indicates a PUSCH transmission beyond the monitoringperiod, the transmission timing determining unit 808 may determine totransmit the configured PUSCH at the indicated timing. Therefore,according to the present disclosure, a D2D signal reception is onlyperformed during the monitoring period and thus self-interference causedby a PUSCH transmission may not occur.

The BS 850 includes a Radio Frequency (RF) unit 855, a processor 860,and a memory 865. The memory 865 is connected with the processor 860,and stores various pieces of information for driving the processor 860.The RF unit 855 is connected with the processor 860, and transmitsand/or receives a radio signal. The processor 860 may implement thefunctions, processes, and/or methods proposed in the presentspecifications. In the above described embodiments, the operations ofthe BS 850 may be implemented by the processor 860. The processor 860generates D2D configuration information disclosed in the presentspecification, configures an uplink grant that indicates a PUSCHtransmission, and processes any PUSCH received from a UE.

To this end, the processor 860 includes a D2D configuration informationgenerating unit 861, a UL grant configuring unit 862, and a PUSCHprocessing unit 863. The D2D configuration information generated by theD2D configuration information generating unit 861 may includeinformation associated with a D2D resource pool for the secondtransmission mode. The information associated with the D2D resource poolmay include information associated with a D2D signal monitoring period(monitoring resource information).

The monitoring resource information may include only informationassociated with a period for monitoring D2D signals of D2D UEs thataccess a single operator's network, or may also include both informationassociated with a period for monitoring D2D signals of D2D UEs thataccess the network of the single operator and information associatedwith a period for monitoring D2D signals of D2D UEs that access adifferent operator's network.

The UL grant configuring unit 862 configures an uplink grant indicatingtransmission of a PUSCH. The RF unit 855 transmits an uplink grantconfigured by the UL grant configuring unit 862 to the UE 800. The UE800 that receives the uplink grant transmits the PUSCH using timingindicated by the uplink grant or using retransmission timing, based onthe monitoring resource information. The PUSCH processing unit 863processes the PUSCH received through the RF unit 855.

Referring again to FIG. 4, FIG. 4 illustrates the case in which ameasurement gap is configured from an n+2^(th) subframe to an n+7^(th)subframe for a UE, and the UE receives an uplink grant indicating aninitial PUSCH transmission in an n+4^(th) subframe from a BS in ann^(th) subframe. In this instance, the UE does not transmit a PUSCH inthe n+4^(th) subframe, and transmits the PUSCH in subsequentretransmission timing (that is, an n+12^(th) subframe).

In this instance, the UE calculates a code rate to be different, basedon different N_(SRS) values, when calculating a code rate fortransmission of a UCI on the PUSCH. Also, rate matching associated withthe corresponding PUSCH may be performed differently based on an N_(SRS)value. Rate matching refers to matching the amount of data to betransmitted for each transmission unit time (e.g., TTI) to the actualmaximum amount of a channel.

Q′ needs to be determined first in order to perform a channel coding ofa CQI, RI information, and HARQ-ACK information. Q′ indicates the numberof coded modulation symbols for each layer. A coding unit may determineQ′ based on a Modulation Coding Scheme (MCS) level applied to a PUSCH,and may control a code rate associated with a CQI, RI, and HARQ-ACKbased on the Q′.

When only one transmission block (e.g., HARQ-ACK or RI information) istransmitted on a PUSCH (that is, single layer transmission), Q′ may becalculated using Equation 1 provided below.

$\begin{matrix}{Q^{\prime} = {\min( {\lceil \frac{O \cdot M_{sc}^{{PUSCH}\text{-}{initial}} \cdot N_{symb}^{{PUSCH}\text{-}{initial}} \cdot \beta_{offset}^{PUSCH}}{\sum\limits_{r = 0}^{C - 1}K_{r}} \rceil, {4 \cdot M_{sc}^{PUSCH}}} )}} & \lbrack {{Equation}\mspace{14mu} 1} \rbrack\end{matrix}$

Here, O (alphabet O) denotes the number of RI bits or the number ofHARQ-ACK bits. M^(PUSCH) _(SC) is a bandwidth scheduled for a PUSCHtransmission in a current subframe for a transmission block, and isexpressed by the number of subcarriers. N^(PUSCH-initial) _(Symb)denotes the number of SC-FDMA symbols in each subframe for an initialPUSCH transmission associated with the same transmission block.N^(PUSCH-initial) _(Symb) may be calculated by Equation 2 providedbelow.

N _(symb) ^(PUSCH-initial)=(2·(N _(symb) ^(UL)−1)−N _(SRS))  [Equation2]

Here, N_(SRS) has a value of 1 or 0. For example, N_(SRS) may be 1 (a)when a UE configured with a single UL serving cell is set to transmit aPUSCH and an SRS in the same subframe for an initial PUSCH transmission;or (b) when a UE transmits a PUSCH and an SRS in the same subframe foran initial transmission and the UE is configured with multiple TimingAdvance Groups (TAGs); or (c) when a PUSCH resource allocation for aninitial transmission even partially overlaps a cell-specific SRSsubframe and bandwidth configuration; or (d) when a subframe for aninitial transmission is a UE-specific type-1 SRS subframe in the sameserving cell; or (e) when a subframe for an initial transmission is aUE-specific type-0 SRS subframe in the same serving cell, and the UE isconfigured with multiple Timing Advance Groups (TAGs). Otherwise,N_(SRS) will be 0.

Referring again to Equation 1 M^(PUSCH-initial) _(SC), C, and Kr may beobtained from an initial PDCCH (or EPDCCH [enhanced-PDCCH]) for the sametransmission block. When an initial PDCCH (or EPDCCH) of downlinkcontrol information (DCI) format 0/4 for the same transmission blockdoes not exist, M^(PUSCH-initial) _(SC), C, and Kr may be determined asfollows. In one example, M^(PUSCH-initial) _(SC), C, and Kr may bedetermined from the latest semi-persistent scheduling-allocated PDCCH(or EPDCCH) when the same transmission block is semi-persistentlyscheduled. In another example, M^(PUSCH-initial) _(SC), C and Kr may bedetermined based on a random access response for the same transmissionblock when the PUSCH is initiated by a random access response grant.

From the perspective of PUSCH rate matching, a PUSCH may be allocatedusing resource elements (REs), excluding: (a) REs for a reference signaltransmission; (b) an SC-FDMA symbol configured for an SRS transmissionwhen a UE is configured with a single cell; (c) a last SC-FDMA symbol inone subframe when a UE is not configured with M-TAG and transmits an SRSin the same subframe; (d) a last SC-FDMA symbol of a subframe to which acell-specific SRS is configured when a PUSCH transmission and acell-specific SRS bandwidth partially or completely overlap; (e) anSC-FDMA symbol reserved for an available SRS transmission in aUE-specific aperiodic SRS subframe on the same serving cell; and (f) anSC-FDMA symbol reserved for an available SRS transmission in aUE-specific periodic SRS subframe and a UE configured with M-TAG.

Referring again to FIG. 4, when a PUSCH transmission indicated by apreviously received uplink grant and an SRS transmission indicated by anRRC signal in a cell are configured on the same subframe in ameasurement gap in DL spectrums/subframes for which a single servingcell is configured, a non-adaptive retransmission operation is appliedand thus a PUSCH may be retransmitted using subsequent retransmissiontiming (that is, n+12^(th) timing) without HARQ-ACK feedback. In thisinstance, when an initial PUSCH and an SRS are configured to transmit inthe same subframe, a UE configured with a single uplink cell may assumeN_(SRS)=1 for a subsequently retransmitted PUSCH. When a UCItransmission occurs at the same time in a subframe where the subsequentretransmission is performed, a UCI code rate is calculated to performmapping (e.g., piggyback) of the corresponding UCI (HARQ-ACK, RI, CQI)to the PUSCH.

Conversely, to receive an inter-PLMN discovery or an inter-carrierdiscovery, a UE configured with D2D discovery may need to monitor acarrier frequency that is different from a carrier frequency that aserving PLMN uses. The present disclosure defines the period as a“monitoring period”. When a D2D signal reception based on a monitoringperiod and a PUSCH transmission based on a previous uplink grant areperformed at the same time, serious self-interference may occur. In thisinstance, an uplink transmission may not be allowed to more reliablyimplement operations of a UE. Therefore, in this instance, the presentdisclosure assumes that a D2D signal reception is performed inpreference to an uplink transmission.

FIGS. 9 and 10 are diagrams illustrating the case in which an initialPUSCH transmission and an SRS transmission are performed in a monitoringperiod according to an embodiment of the present disclosure.

Referring to FIGS. 9 and 10, in the case in which subframes from ann+3^(th) subframe to an n+6^(th) subframe are configured for a UE thatis provided with a first carrier from a first base station (eNB1)belonging to a serving PLMN, as a monitoring period with respect to aD2D signal (e.g., a discovery signal for D2D discovery) of a D2D UE thataccesses a neighboring PLMN: when the UE receives an uplink grantindicating an initial PUSCH transmission in n+4^(th) subframe from thefirst BS in the n^(th) subframe of the first carrier, the UE may processthe uplink grant but may not transmit a PUSCH in the n+4^(th) subframeof the first carrier in order to receive a D2D signal. Subsequently, theUE may transmit the PUSCH, which has not been transmitted, usingsubsequent retransmission timing (that is, an n+12^(th) subframe)without HARQ feedback, through the non-adaptive retransmission. However,a serving BS may not be aware of information associated with themonitoring period of the UE. Inter-PLMN cooperation is difficult. Also,only a corresponding inter-PLMN discovery UE is capable of obtainingcorresponding resource information on a different PLMN carrier throughan initial cell search. To overcome the limit, a serving PLMN may obtaininformation associated with a D2D discovery resource of a different PLMNby performing inter-PLMN cooperation in advance or by executing a methodin which an inter-PLMN discovery UE obtains corresponding resourceinformation on a different PLMN carrier through an initial cell searchand reports the same to the serving PLMN. Therefore, in this situation,a serving BS (serving PLMN) provides an uplink grant to a UE and a PUSCHmay be transmitted using subsequent retransmission timing (that is, ann+12^(th) subframe) in response to the uplink grant (when retransmissionis required), irrespective of whether the serving PLMN obtains discoveryinformation of a different PLMN or not. In this instance, assumptionsassociated with a code rate of a UCI and a PUSCH rate matching may bedifferent between a BS and a UE. For example, a UE is configured withM-TAG for one or more uplink cells (UL CA) for a PUSCH transmission, andan initial PUSCH and a type 0 SRS (periodic SRS) are on the samesubframe of the same serving cell, and an SRS is configured to betransmitted in an n+4^(th) subframe although the SRS has not beenactually transmitted. Using an assumption of a UCI code rate of theserving BS under the situation, when an indication that indicates aninitial PUSCH transmission in a monitoring period including a subframe(n+4^(th) subframe) configured with a type 0 SRS subframe is received,the serving PLMN assumes N_(SRS)=1 for a retransmitted PUSCH in aretransmission subframe, calculates a UCI code rate and rate matching,and performs decoding. Conversely, a UCI code rate and rate matching ona retransmission of an inter-PLMN discovery UE are calculated andtransmitted by assuming N_(SRS)=0 for a PUSCH retransmission because aPUSCH and an SRS are not transmitted in the n+4^(th) subframe fordiscovery monitoring.

Therefore, if the BS receives a UCI on a PUSCH retransmission of the UEthat assumes a different UCI code rate in an n+12^(th) subframe, it maynot successfully perform UCI decoding because the UE transmits a UCIthat does not match the number of UCI symbols that the BS is aware of.It is difficult to embody a BS that can perform blind decoding withrespect to N_(SRS)=0 or 1 to cope with the above described situation,because there is no information associated with an actual monitoringperiod and the BS needs to perform blind decoding with respect to alluplink subframes, which is a drawback. This may cause the BS to performunnecessary calculation and thus complexity may dramatically increase.

To overcome this drawback, in the present disclosure, when a UEconfigured with one or more uplink cells is set to transmit (but doesnot actually transmit) an initial PUSCH and an SRS in the same subframeof the same serving cell in the monitoring period, rate matchingassociated with the calculation of a UCI code rate is set to alwaysperform based on N_(SRS)=0 or N_(SRS)=1 using the retransmission timingof the corresponding PUSCH. The SRS corresponds to a UE-specific type-1SRS subframe or a UE-specific type-0 SRS subframe, and the correspondingUE is configured with M-TAG. Although the above description has beenprovided for the purpose of calculating a UCI code rate, the sameoperations can also be described from the perspective of PUSCH ratematching. For example, when a UE configured with one or more uplinkcells is set to transmit (but does not actually transmit) an initialPUSCH and an SRS on the same subframe of the same serving cell in themonitoring period, rate matching associated with a correspondingretransmitted PUSCH may allocate a PUSCH (N_(SRS)=0) or may not allocatea PUSCH (N_(SRS)=1) to a last SC-FDMA symbol, using the retransmissiontiming of the corresponding PUSCH.

Although it is assumed that a serving cell (or a serving PLMN) is notaware of information associated with the monitoring period, the servingcell may be aware of the information occasionally through other signalsor reports from a UE. In this instance, calculation of a UCI code rateon a retransmitted PUSCH and rate matching associated with thecorresponding retransmitted PUSCH may be set to always be performedbased on N_(SRS)=0 or N_(SRS)=1 in the above described situation. Thisis to prevent the problem described above, which may be caused byanother assumption and the embodiment of a scheduler, from occurring.

Therefore, a serving BS and a UE that performs an inter-PLMN discoverymay have the same information associated with the code rate (the numberof UCI symbols) of a UCI transmitted during a retransmission under theassumption provided in the environment of FIGS. 9 and 10. Accordingly,the system may avoid both an increase in the complexity of the UCIdecoding operation of the BS and a waste of resources (a probability ofnot utilizing a last SC-FDMA symbol), and may therefore effectivelyutilize uplink resources, and thus, the overall system may increaseuplink performance.

A method of setting the calculation of a UCI code rate and rate matchingassociated with a corresponding retransmitted PUSCH to be performedbased on N_(SRS)=0 or N_(SRS)=1, using the retransmission timing of thecorresponding PUSCH, will be described as follows.

When only one transmission block, for example, HARQ-ACK or RIinformation, is transmitted on a PUSCH (that is, single layertransmission), Q′ may be calculated by Equation 3 provided below.

$\begin{matrix}{Q^{\prime} = {\min {\quad( {\lceil \frac{O \cdot M_{sc}^{{PUSCH} - {initial}} \cdot N_{symb}^{{PUSCH} - {initial}} \cdot \beta_{offset}^{PUSCH}}{\sum\limits_{r = 0}^{C - 1}\; K_{r}} \rceil,{4 \cdot M_{sc}^{PUSCH}}} )}}} & \lbrack {{Equation}\mspace{14mu} 3} \rbrack\end{matrix}$

Here, O (alphabet O) denotes the number of RI bits or the number ofHARQ-ACK bits. M^(PUSCH) _(SC) is a bandwidth scheduled for a PUSCHtransmission in the current subframe of a transmission block, and isexpressed by the number of subcarriers. N^(PUSCH-initial) _(Symb)denotes the number of SC-FDMA symbols for each subframe for an initialPUSCH transmission associated with the same transmission block.N^(PUSCH-initial) _(Symb) may be calculated by Equation 3 providedbelow.

N _(symb) ^(PUSCH-initial)=(2·(N _(symb) ^(UL)−1)−N _(SRS))  [Equation4]

Here, N_(SRS) has a value of 1 or 0. For example, N_(SRS) may be 1 (a)when a UE configured with one or more uplink cells transmits a PUSCH andan SRS for an initial transmission in the same subframe; (b) when aPUSCH resource allocation for an initial transmission even partiallyoverlaps a cell-specific SRS subframe and bandwidth configuration; (c)when a subframe for an initial transmission is a UE-specific type-1 SRSsubframe; or (d) when a subframe for an initial transmission is aUE-specific type-0 SRS subframe and a UE is configured with TimingAdvance Groups (TAGs). Otherwise, N_(SRS) will be 0.

Referring again to Equation 3 M^(PUSCH-initial) _(SC), C, and Kr may beobtained from an initial PDCCH (or enhanced-PDCCH [EPDCCH]) for the sametransmission block. When an initial PDCCH (or EPDCCH) of downlinkcontrol information (DCI) format 0 for the same transmission block doesnot exist, M^(PUSCH-initial) _(sc), C, and Kr may be determined asfollows. In one example, M^(PUSCH-initial) _(sc), C, and Kr may bedetermined from the latest semi-persistent scheduling-allocated PDCCH(or EPDCCH) when the same transmission block is semi-persistentlyscheduled. In another example, M^(PUSCH-initial) _(sc), C, and Kr may bedetermined based on a random access response for the same transmissionblock when the PUSCH is initiated by a random access response grant.

FIG. 11 is a flowchart illustrating the operations of a BS and a D2D RxUE according to an embodiment of the present disclosure.

Referring to FIG. 11, a BS transmits configuration informationassociated with D2D discovery and communication to a UE in a cell inoperation S1110. The D2D configuration information may be transmitted tothe UE for D2D discovery or D2D data transmission through, for example,a System Information Block (SIB) or a dedicated RRC signal. Theinformation associated with a D2D resource pool may include informationassociated with a D2D signal monitoring period (monitoring resourceinformation).

For example, monitoring resource information may include onlyinformation associated with a period for monitoring D2D signals of D2DUEs that access a single operator's network. Alternatively, themonitoring resource information may additionally include informationassociated with a period for monitoring D2D signals of D2D UEs thataccess the single operator's network, and information associated with aperiod for monitoring D2D signals of D2D UEs that access a differentoperator's network.

The BS transmits, to the UE, an uplink grant indicating transmission ofa PUSCH in operation S1120.

The UE that receives the uplink grant determines monitoring resourceinformation (information associated with a resource to be monitored bythe UE for D2D communication) in operation S1130. When an indicatedperiod for transmission of the PUSCH and SRS overlaps a resource(subframe) to be monitored, the PUSCH and SRS may not be transmitted inthe corresponding period.

When the indicated period for transmission of the PUSCH and SRS isincluded in the resource to be monitored and a UCI transmission occursat the same time in a retransmission PUSCH subframe, a UCI code rate forthe retransmitted PUSCH is calculated and PUSCH rate matching isperformed based on the above described assumption in operation S1140.The UCI code rate calculation and PUSCH rate matching are performedbased on a set N_(SRS) value, and N_(SRS) may have a value of 1 or 0.

In operation S1140, when the UCI code rate calculation and PUSCH ratematching are performed, the UE transmits a PUSCH including the UCI tothe BS in operation S1150.

FIG. 12 is a block diagram illustrating a wireless communication systemaccording to an embodiment of the present disclosure.

Referring to FIG. 12, a wireless communication system that supports D2Dcommunication may include a UE 1200 and a BS (or cluster head 1250).

The UE 1200 includes a processor 1205, a Radio Frequency (RF) unit 1210,and a memory 1215. The memory 1215 is connected with the processor 1205,and stores various pieces of information for driving the processor 1205.The RF unit 1210 is connected with the processor 1205, and transmitsand/or receives a radio signal. For example, the RF unit 1210 mayreceive, from the BS 1250, D2D configuration information disclosed inthe present specifications and an uplink grant indicating a PUSCHtransmission. Also, the RF 1210 unit may transmit a PUSCH to the BS 1250using timing indicated by the uplink grant or retransmission timing.

The memory 1215 may store D2D configuration information, resource poolinformation for the second transmission mode, and information associatedwith a period for monitoring reception of a D2D signal, and may providethe information to the processor 1205 at the request of the processor1205.

The processor 1205 may implement functions, processes, and/or methodsproposed in the present specification. Particularly, the processor 1205may implement all of the operations of FIG. 3. In one example, theprocessor 1205 may include a monitoring unit 1206, a code ratecalculating unit 1207, and a rate matching unit 1208.

The monitoring unit 1206 may monitor a D2D signal during a monitoringperiod configured based on information associated with a monitoringperiod for D2D signal reception. The monitoring unit 1206 determineswhether an uplink grant indicating a PUSCH transmission in themonitoring period is received.

The code rate calculating unit 1207 calculates a UCI code rate when anindicated period for transmission of a PUSCH is not included in themonitoring period.

The rate matching unit 1208 performs PUSCH rate matching.

Therefore, according to the present disclosure, D2D signal reception isonly performed during the monitoring period and thus self-interferencecaused by a PUSCH transmission may not occur.

The BS 1250 includes a Radio Frequency (RF) unit 1255, a processor 1260,and a memory 1265. The memory 1265 is connected with the processor 1260,and stores various pieces of information for driving the processor 1260.The RF unit 1255 is connected with the processor 1260, and transmitsand/or receives a radio signal. The processor 1260 may implement thefunctions, processes, and/or methods proposed in the presentspecifications. In the above described embodiments, the operations ofthe BS 1250 may be implemented by the processor 1260. The processor 1260generates D2D configuration information disclosed in the presentspecification, configures an uplink grant that indicates a PUSCHtransmission, and processes a PUSCH received from a UE.

To this end, the processor 1260 includes a D2D configuration informationgenerating unit 1260, a UL grant configuring unit 1262, and a PUSCHprocessing unit 1263. The D2D configuration information generated by theD2D configuration information generating unit 1261 may includeinformation associated with a D2D resource pool for the secondtransmission mode. The information associated with the D2D resource poolmay include information associated with a D2D signal monitoring period(monitoring resource information).

The monitoring resource information may include only informationassociated with a period for monitoring D2D signals of D2D UEs thataccess a single operator's network, or may additionally include bothinformation associated with a period for monitoring D2D signals of D2DUEs that access a single operator's network and information associatedwith a period for monitoring D2D signals of D2D UEs that access adifferent operator's network.

The UL grant configuring unit 1262 configures an uplink grant indicatingtransmission of a PUSCH. The RF unit 1255 transmits, to the UE 1200, anuplink grant configured by the UL grant configuring unit 1262. The UE1200 that receives the uplink grant transmits the PUSCH and SRS usingtiming indicated by the uplink grant or retransmission timing, based onmonitoring resource information. The PUSCH processing unit 1263processes the PUSCH received through the RF unit 1255.

An Automatic Repeat Request (ARQ) is a technology used for increasingreliability of radio communication. According to ARQ, a transmitterretransmits a data signal when a receiver fails to receive a datasignal. Hybrid Automatic Repeat Request (HARQ) is a combination ofForward Error Correction (FEC) and ARQ. A receiver that uses HARQbasically attempts error correction with respect to a received datasignal, and determines whether to execute retransmission using an errordetection code. The error detection code may use a Cyclic RedundancyCheck (CRC). When an error in a data signal is not detected through theCRC detection process, the receiver determines that decoding the datasignal was successful. In this instance, the receiver transmits anAcknowledgement (ACK) signal to the transmitter. When an error in a datasignal is detected through the CRC detection process, the receiverdetermines that decoding the data signal has failed. In this instance,the receiver transmits a Not-Acknowledgement (NACK) signal to thetransmitter. The transmitter may retransmit a data signal when the NACKsignal is received.

A BS transmits a PDCCH including a UL grant for a PUSCH transmission ofa UE; the UE transmits UL data through a PUSCH using determined timing;and the BS transmits a HARQ ACK/NACK with respect to the UL data througha PHICH using determined timing. UL HARQ refers to a process thatrepeats the above process until the UE receives an ACK signal from theBS.

The MAC layer may control a HARQ process, may execute mapping between alogical channel and a transport channel, and may execute multiplexing ordemultiplexing of a MAC Service Data Unit (SDU) that belongs to thelogical channel of transport blocks (TBs) provided to a physical channelon a transport channel. The MAC layer may provide a service to an RLClayer through a logical channel. The logical channel is classified intoa control channel for transferring control area information and atraffic channel for transferring user area information. For example,services provided from the MAC layer to a higher layer include a datatransfer service or a radio resource allocation service.

FIG. 13 is a diagram illustrating a structure of an MAC entity of a UE.

Referring to FIG. 13, an MAC entity may perform various functions, suchas logical channel prioritization, multiplexing/demultiplexing, HARQ,random access controlling, or the like. Particularly, the MAC entityperforms mapping between logical channels and transport channels, andmay perform multiplexing of MAC SDUs onto transport blocks (TBs) to bedelivered to the physical layer on the transport channels from one orvarious (different) logical channels. The MAC entity may performdemultiplexing of MAC SDUs onto transport blocks (TBs) delivered fromthe physical layer on transport channels from one or various (different)logical channels. The MAC entity may perform scheduling informationreporting. The MAC entity may perform error correction through HARQ. Inthis instance, a part that performs the error correction through HARQmay be referred to as a HARQ entity. Also, the MAC entity may handleprioritization among UEs through dynamic scheduling, and the MAC entitymay handle prioritization among logical channels of a single UE. The MACentity may perform logical channel prioritization, and may select atransport format.

The MAC entity may receive, from a lower physical layer, a datatransmission service, a HARQ feedback signal, a scheduling requestsignal, a measurement (e.g., channel quality indication [CQI]), or thelike, and may process the same.

Recently, a method of supporting D2D communication has been considered,wherein UEs utilize transmission/reception technologies of a wirelesscommunication system in the frequency band of the wireless communicationsystem or in other bands, and directly exchange user data between theUEs without passing through infrastructure (for example, a BS). D2Dcommunication may allow wireless communication in an area outside thatcovered by limited wireless communication infrastructure, and may reduceload on the network of the wireless communication system. Also, D2Dcommunication may provide disaster information to UEs even when BSs donot operate smoothly in war or disaster situations, which is anadvantage.

A UE that transmits a signal based on the D2D communication is definedas a transmission UE (Tx UE), and a UE that receives a signal based onthe D2D communication is defined as a reception UE (Rx UE). The Tx UEtransmits a discovery signal, a D2D control signal, or a D2D datasignal. The Rx UE receives a discovery signal, a D2D control signal, ora D2D data signal. The Tx UE and the Rx UE may operate by exchangingtheir roles. A signal transmitted by the Tx UE may be received by two ormore Rx UEs. Alternatively, signals transmitted by two or more Tx UEsmay be selectively received by a single Rx UE. A D2D signal may betransmitted through an uplink resource. Therefore, a D2D signal may bemapped to an uplink subframe and may be transmitted from the Tx UE tothe Rx UE. The Rx UE may receive a D2D signal on the uplink subframe.

FIG. 14 is a diagram illustrating the concept of cellular network-basedD2D communication according to the present disclosure.

Referring to FIG. 14, a cellular communication network including a firstBS 1410, a second BS 1420, and a first cluster 1430 is configured. Afirst UE 1411 and a second UE 1412 included in a cell provided by thefirst BS 1410 may execute communication through a general access link(cellular link) through the first BS 1410. This is anin-coverage-single-cell D2D communication scenario. The first terminal1411 included in the first BS 1411 may execute D2D communication with afourth UE 1421 included in the second BS 1420. This is anin-coverage-multi-cell D2D communication scenario. Also, a fifth UE 1431belonging outside of a network coverage area may generate the singlecluster 1430 with a sixth UE 1432 and a seventh UE 1433, and may performD2D communication with them. This is an out-of-coverage D2Dcommunication scenario. Here, the fifth UE 1450 may operate as a clusterhead (CH) of a first cluster. A cluster head is a UE (or unit) used as areference for at least the purpose of synchronization and, occasionally,allocates a resource for different purposes. The cluster header mayinclude an Independent Synchronization Source (ISS) for thesynchronization of an out-of-coverage UE. Also, the third UE 1413 mayperform D2D communication with the sixth UE 1432, which corresponds to apartial-coverage D2D communication scenario.

D2D communication may include direct communication that directlytransmits and receives D2D control information and/or user data. Tosupport the D2D communication, a D2D discovery procedure and a D2Dsynchronization procedure may be executed. D2D communication may be usedfor various purposes. For example, D2D communication within a networkcoverage area and D2D communication outside a network coverage area maybe used for public safety. D2D communication outside a network coveragearea may be used for only the public safety.

To perform D2D data transmission/reception through D2D communication,D2D control information needs to be transmitted/received between UEs.D2D control information may be referred to as a Scheduling Assignment(SA) or D2D SA. A D2D Rx UE may perform a D2D data reception based onthe SA. The SA may include, for example, at least one out of: New DataIndicator (NDI), a Target Identification (target ID), a RedundancyVersion (RV) indicator, a Modulation and Coding Scheme (MCS) indication,a Resource Pattern for Transmission (RPT) indication, and a powercontrol indication.

Here, the NDI indicates whether a current transmission is a repetitionof data, that is, a retransmission, or a new transmission. A receivermay combine the same data based on the NDI. The target ID indicates anID of a terminal to which a corresponding data MAC PDU is intended to betransmitted. The data MAC PDU may be transmitted through group castingor broadcasting based on the ID value, and may be transmitted eventhrough uni-casting based on the settings. The RV indicator indicates aredundancy version by specifying different start points in a circularbuffer for encoded buffer reading. A Tx UE may choose various redundancyversions associated with a repeated transmission of the same packet,based on the RV indicator. The MCS indication indicates an MCS level forD2D communication. However, an MCS for D2D communication (e.g., SA ordata) may be fixed to QPSK. The RPT indication indicates atime/frequency physical resource in which corresponding D2D data isallocated and transmitted. The power control indication is aninstruction used when a UE that receives corresponding informationcontrols the magnitude of power to be appropriate for a correspondingD2D transmission.

From the perspective of a Tx UE, the Tx UE may perform resourceallocation for D2D communication in two modes.

In mode 1 a BS or a relay node (hereinafter a BS includes a relay node)schedules a predetermined resource(s) for D2D communication. That is, inmode 1, a predetermined resource(s) used for transmitting D2D data andD2D control information from a Tx UE may be designated by a BS or by arelay node. In Mode 2 a UE directly selects a predetermined resource(s)from a resource pool. That is, in mode 2, a Tx UE directly selects apredetermined resource(s) to be used for transmitting D2D data and D2Dcontrol information.

A D2D communication-enabled UE must support mode 1 for in-coverage D2Dcommunication. A D2D communication-enabled UE may support mode 2 forout-of-coverage or edge-of-coverage D2D communication.

In mode 1, the location of a resource(s) for a D2D control informationtransmission and the location of a resource(s) for a D2D datatransmission are given by a BS. That is, when the BS gives a UE the samegrant for D2D SA and data transmission, the BS transmits an (E)PDCCH ina DCI message format having a size identical to that of DCI format 0. Inmode 2, a resource pool for transmission of D2D control information(e.g., SA) may be pre-configured and/or may be semi-staticallyallocated. In this instance, a Tx UE may select a resource for D2Dcontrol information from the resource pool, for transmission of the D2Dcontrol information.

D2D discovery may be performed on a D2D discovery resource. For example,a D2D UE may transmit a discovery signal through a randomly selecteddiscovery resource (hereinafter referred to as a D2D discoveryresource), within each discovery period. For example, a discovery periodand a discovery resource in a network coverage area may be configured bya BS. Outside the network coverage area, a discovery resource may beselected based on a period and an offset set by a Tx UE, or a discoveryresource may be selected based on a pre-configured (or configured)nominal transmission probability or a fixed (or adaptive) transmissionprobability. A single D2D discovery resource may consist of n contiguousPRBs in the frequency domain and a single subframe. In this instance,inter-slot frequency hopping may not be performed in the subframe. n maybe, for example, 2 or 3. A set of D2D resources may be used for arepeated transmission of a Medium Access Control Protocol Data Unit (MACPDU) that delivers a discovery signal (hereinafter referred to as adiscovery MAC PDU) within a discovery period. A plurality of D2Ddiscovery resource sets may exist within a single discovery period, andD2D discovery resources in a single D2D discovery resource set may becontiguous or non-contiguous in the time domain, and may be deployedbased on frequency hopping in the frequency axis (inter-subframefrequency hopping). From the perspective of an Rx UE, a discovery signalmay be monitored in a resource pool for D2D reception.

A D2D discovery period may be classified as type 1 or type 2B accordingto a discovery period. Type 1 indicates periodicity of resourcesallocated for D2D discovery signal transmission within a cell. Type 2Bindicates periodicity of resources for D2D signal reception from a cell.Multiple discovery periods having various lengths may be used. In type2B, a network may configure a predetermined resource for transmission ofa D2D discovery signal.

D2D discovery and communication may be operated independently from aWide Area Network (WAN). In some instances, WAN signal is transmitted toa D2D UE from a BS through a DL spectrum and, at the same time, a D2Dsignal may be transmitted from another UE. A Wide Area Network (WAN)refers to a network that configures a wide coverage area in an existingcellular network and provides mobile UEs with voice/data traffic, andmay include, for example, WCDMA, LTE, WiMax, and the like. A radioaccess network as described above is generally referred to as a WAN. AUE having a single transceiver chain is incapable of transmitting orreceiving signals through multiple frequency bands at the same time.Therefore, when a WAN signal is transmitted from a BS through a DLspectrum and a D2D signal is simultaneously transmitted from another UE,prioritization of signals to be processed must be defined, and handlingof low-priority signals must also be defined.

Particularly, the present disclosure intensively describes a method ofhandling a case in which a D2D (Rx) resource pool for D2D signalreception and the reception timing of a PHICH that carries a HARQ-ACKsignal overlap in the time axis.

When a D2D (Rx) resource pool is configured (e.g., type 1/2 D2Ddiscovery) in the reception timing of a (WAN) PHICH in response to aPUSCH transmission, a D2D UE having a single transceiver chain mayreceive a D2D signal (e.g., D2D discovery, SA, or D2D data), and may notreceive a PHICH. Particularly, when a D2D signal corresponds to a type1/2 discovery Tx/Rx signal, a mode 2 SA Tx/Rx signal, or the like, thecorresponding D2D signal may have a higher priority than a DL signal(e.g., PHICH) on a WAN DL spectrum.

FIG. 15 is a diagram illustrating an example of a DL subframe in which aUE is incapable of receiving a PHICH according to the presentdisclosure. FIG. 15 assumes a case in which an uplink transmission and adownlink transmission are based on a Frequency Division Duplex (FDD)scheme.

Referring to FIG. 15, UL subframes #n+7 to #n+10 are configured as a D2DRx resource pool (i.e., a monitoring period for a D2D signal hereinafterreferred to as a D2D monitoring period), and a UE can receive an initialUL grant that indicates a PUSCH transmission in a UL subframe #n+4 froma BS (or a network) in a subframe #n. Here, the D2D monitoring periodmay include a Tx/Rx resource set/resource pool for D2D discovery or D2Dcommunication. The UE transmits an initial PUSCH to the BS in the ULsubframe #n+4 based on the UL grant. The BS generates a HARQ ACK/NACKsignal indicating whether the PUSCH was successfully received andtransmits the same to the UE in a DL subframe #n+8. In a WAN system, ULHARQ supports a synchronized HARQ. That is, it is indicated that thetiming of an initial UL grant transmission from the BS, the timing of aUL data transmission from the UE, and the timing of a HARQ ACK/NACKsignal indication made by the BS are all predetermined.

However, as described above, the UL subframes #n+7 to #n+10 areconfigured as a D2D monitoring period and the UE needs to receive (orperform blind decoding of) a D2D signal, and thus, the UE may not expectreception of a PHICH in the DL subframe #n+8. Originally, the UE wassupposed to obtain HARQ ACK/NACK information based on a PHICH receivedin a physical layer of a UL subframe #n+8, which was based on asynchronized UL HARQ timing, and to transmit the HARQ ACK/NACKinformation to a higher layer (e.g., a MAC layer). However, the UE failsto receive the PHICH in the UL subframe #n+8 and thus may not properlyperform a UL HARQ procedure. This is similar to the case in which ameasurement gap is configured for the UE.

FIG. 16 is a diagram illustrating an example of a measurement gap in aWAN system according to the present disclosure.

Generally, a UE performs measurement in order to recognize whetherneighboring cells exist, an intensity of a signal, and the like. In thisinstance, neighboring cells existing in the intra-frequency zone cantransmit a signal through the same frequency band as that of a currentserving cell. Therefore, the UE is capable of performing measurements inassociation with neighboring cells, while proceeding with transmissionand reception in the serving cell. However, neighboring cells existingin the inter-frequency zone transmit a signal through a frequency banddifferent from that of the serving cell and thus, the UE temporallyinterrupts the transmission and reception executed with the currentserving cell during the measurement gap, retunes a Radio Frequency (RF)chain, and receives a signal associated with a frequency band that isrecognized to have a probability of including neighboring cells. The UEmay perform a measuring operation with respect to neighboring cellsexisting in the inter-frequency zone by utilizing a periodic measurementgap unless the UE has more than one (Rx) RF chain.

The measurement gap may be classified as a first gap pattern that isrepeated based on a period of 40 ms and has a length of 6 ms, and asecond gap pattern that is repeated based on a period of 80 ms and has alength of 6 ms. Generally, a network may configure one of the twopatterns for the UE.

A trade-off exists between the first pattern and the second pattern inTable 1. The first pattern has a short period but affects a WANtransmission and reception through a serving cell. Conversely, thesecond pattern has a longer period than the first pattern, but lessfrequently affects the WAN transmission and reception through theserving cell.

A UE may not transmit any data to the BS during a measurement gap. Also,a UE may not expect tuning of an (Rx) RF chain to a WAN carrierfrequency during a measurement gap. That a UE is incapable of receivinga WAN signal during a measurement gap, is similar to the case in which aUE is incapable of receiving a WAN signal during a D2D monitoringperiod.

Due to a period or a gap where reception of a WAN signal (e.g., PHICH)is not allowed (or is not expectable) as described above, the UE doesnot receive a WAN signal which is transmitted based on predeterminedtiming. Therefore, there is a desire for a method for handling the same.

The present disclosure proposes a method of handling a corresponding ULHARQ procedure under the assumption that the WAN signal includes a PHICHthat carries a HARQ-ACK.

FIG. 17 is a diagram illustrating a UL HARQ operation according to anembodiment of the present disclosure.

Referring to FIG. 17, when PHICH reception timing overlaps a D2Dmonitoring period, the UE will determine that a corresponding PHICHindicates ACK. That is, although the UE will fail to receive a PHICH,the UE may assume that a BS successfully received a PUSCH transmitted ina UL subframe #+4.

For example (alt 1-1), D2D discovery (type 1/2B) or D2D communication(mode 1/2) is configured or enabled for the UE and a DL subframe (e.g.,DL subframe #n+8) associated with PHICH reception in response to aprevious PUSCH transmission overlaps a D2D monitoring period (a Tx/Rxresource set/resource pool for D2D discovery or D2D communication), thecorresponding UE does not expect a PHICH reception in the correspondingDL subframe, and transfers an ACK signal with respect to a transmissionblock (TB) associated with the PUSCH to a higher layer (MAC layer). Thismay be executed in a physical (PHY) layer of the UE.

This is a method in which the UE always regards that ACK is indicatedfor a corresponding TB and transfers the ACK information to a higherlayer (MAC layer) from the PHY layer even though the UE fails to receivea PHICH because PHICH reception timing and a D2D monitoring periodoverlap. This is a method for the physical layer of the UE to alwaystransfer ACK to a higher layer and to process a UL HARQ procedurebecause the BS has a high probability of successfully receiving a PUSCHtransmission (that is, ACK). As a matter of course, NACK may be includedin the corresponding PHICH. In this instance, this may be covered basedon an ARQ operation of an RLC layer.

In another example (alt 1-2), when D2D discovery (type 1/2B) or D2Dcommunication (mode 1/2) is configured or enabled, a DL subframe (e.g.,DL subframe #n+8) associated with a PHICH reception in response to aprevious PUSCH transmission overlaps a D2D monitoring period (a Tx/Rxresource set/resource pool for D2D discovery or D2D communication), anda MAC PDU for the corresponding PUSCH transmission is not obtained froman Msg3 buffer, “HARQ_FEEDBACK”, which is a state variable associatedwith a HARQ process (in MAC) of the corresponding UE, is set to ACK.This may be performed in a MAC layer (or MAC entity) of the UE. Here,the Msg3 buffer is a buffer for transmitting Msg3, and a MAC PDU may begenerated in the Msg3 buffer according to a UL grant (in PDSCH) receivedbased on a Random Access Response (by PDCCH) in a random accessprocedure. That is, the present embodiment indicates that the MAC PDUfor a PUSCH transmission is different from the MAC PDU generated in arandom access procedure.

This is a method of processing a HARQ procedure by the MAC layer whichacts as a main body. When an ACK/NACK signal transferred from the PHYlayer does not exist, the HARQ procedure may be processed through theoperations of the MAC layer proposed above.

FIG. 18 is a diagram illustrating a UL HARQ operation according toanother embodiment of the present disclosure.

Referring to FIG. 18, when PHICH reception timing overlaps a D2Dmonitoring period, a UE may determine that a corresponding PHICHindicates NACK. That is, even though the UE failed to receive the PHICH,the UE may assume that a BS failed to successfully receive a PUSCHtransmitted in a UL subframe #+4.

For example (alt 2-1), when D2D discovery (type 1/2B) or D2Dcommunication (mode 1/2) is configured or enabled for the UE and when aDL subframe (e.g., DL subframe #n+8) associated with a PHICH receptionin response to a previous PUSCH transmission overlaps a D2D monitoringperiod (a Tx/Rx resource set/resource pool for D2D discovery or D2Dcommunication), the corresponding UE does not expect PHICH reception inthe corresponding DL subframe, and transfers a NACK signal with respectto a transmission block (TB) associated with the PUSCH to a higher layer(MAC layer). This may be executed in a physical (PHY) layer of the UE.

As another example (alt 2-2), when D2D discovery (type 1/2B) or D2Dcommunication (mode 1/2) is configured or enabled, a DL subframe (e.g.,DL subframe #n+8) associated with PHICH reception in response to aprevious PUSCH transmission overlaps a D2D monitoring period (a Tx/Rxresource set/resource pool for D2D discovery or D2D communication), anda MAC PDU for the corresponding PUSCH transmission is not obtained froman Msg3 buffer, a HARQ entity indicates/performs a non-adaptiveretransmission associated with the corresponding PUSCH withpredetermined timing. This may be performed in a MAC layer (or MACentity) of the UE. Here, the non-adaptive retransmission indicatesretransmission of the corresponding PUSCH based on the same format asthe previous transmission (e.g., the same MAC level, transmission power,and the like).

In this instance, without a separate indication from the physical layer,the MAC layer may indicate/performs non-adaptive retransmission.Although the BS actually indicates ACK through the PHICH, the UE willperform a PUSCH retransmission. This assumes a case in which the BSfails to receive a previous PUSCH transmission and indicates NACKthrough a PHICH, thereby preventing unnecessary packet loss in a higherlayer (RLC layer). This may be appropriate for system operation that isconservative or that prioritizes reliability.

The above described operations according to the present disclosure maybe applied to a multi-carrier environment, particularly, a carrieraggregation (CA) environment.

FIGS. 19 and 20 are diagrams illustrating UL HARQ operations in a systemin which carrier aggregation is configured.

As illustrated in FIGS. 19 and 20, when a D2D UE operates based on halfduplex in a plurality of carriers in TDD, PHICH reception and D2Dtransmission may overlap in the time axis and a PHICH may not bereceived (according to the half duplex rule). In this instance, a UEdetermines that the corresponding PHICH indicates ACK (FIG. 19), and mayperform a UL HARQ operation based on the same. Alternatively, the UEdetermines that the corresponding PHICH indicates NACK (FIG. 20), andmay perform a UL HARQ operation based on the same.

FIG. 21 is a flowchart illustrating a UL HARQ-performing method when aD2D monitoring period and PHICH reception timing overlap.

Referring to FIG. 21, a BS and D2D UEs perform a D2D configurationprocedure in operation S2100. In this instance, a Tx UE and an Rx UEamong the D2D UEs may receive D2D configuration information from the BS.Here, the Tx UE and the Rx UE are relative concepts for D2Dcommunication. The D2D configuration information may be transmittedthrough a System Information Block (SIB), or may be transmitted throughRadio Resource Control (RRC) signaling. The Tx UE and the Rx UE maydetermine/detect a D2D monitoring period based on the D2D configurationinformation.

The Rx UE receives a UL grant from the BS in operation S2110. The ULgrant may be received through a PDCCH/EPDCCH. The UL grant may indicatea PUSCH transmission in a first timing. The Rx UE transmits a PUSCH tothe BS in the first timing based on the UL grant in operation S2120.

The Tx UE transmits a D2D signal based on the D2D configurationinformation in operation S2130. Here, the D2D signal includes a D2Ddiscovery signal and a D2D communication signal. The D2D communicationsignal includes SA and D2D data.

The BS transmits a PHICH indicating HARQ ACK/NACK with respect to thePUSCH based on whether the BS successfully receives the PUSCH, to the RxUE at a second timing in operation S2140.

When a D2D monitoring period and second timing for the PHICH receptionoverlap, the Rx UE expects reception of a D2D signal and does not expectreception of a PHICH. That is, the Rx UE does not receive the PHICH,determines HARQ ACK/NACK with respect to the PUSCH according to thepredetermined standard, and performs a UL HARQ operation based on thisdetermination in operation S2150.

For example, when the D2D monitoring period and second timing overlap,it may be determined that the corresponding PHICH indicates ACK. In thisinstance, the physical layer of the UE does not expect reception of aPHICH in a DL subframe of the corresponding second timing, and maytransfer an ACK signal with respect to a transmission block (TB)associated with the PUSCH to a higher layer, e.g., MAC layer, (alt 1-1).Alternatively, when a MAC PDU for the corresponding PUSCH transmissionis not obtained from an Msg3 buffer, the MAC layer (or MAC entity) ofthe UE may set “HARQ_FEEDBACK”, which is a state variable associatedwith the HARQ process of a corresponding UE, to ACK (alt 1-2).

As another example, when the D2D monitoring period and second timingoverlap, it may be determined that the corresponding PHICH indicatesNACK. In this instance, the physical layer of the UE does not expectreception of a PHICH in a DL subframe of the corresponding secondtiming, and may transfer a NACK signal with respect to a transmissionblock (TB) associated with the PUSCH to a higher layer, e.g., MAC layer,(alt 2-1). Alternatively, when a MAC PDU for the corresponding PUSCHtransmission is not obtained from an Msg3 buffer, the MAC layer (or MACentity) may indicate/perform a non-adaptive retransmission of thecorresponding PUSCH with timing determined by the HARQ entity (alt 2-2).

FIG. 22 is a flowchart illustrating the operations of a UE according tothe present disclosure. In FIG. 22, the UE may correspond to the Rx UEof FIG. 21.

Referring to FIG. 22, the UE receives D2D configuration information inoperation S2200. The UE may receive the D2D configuration informationfrom a BS, or may receive the D2D configuration information throughanother D2D UE. The UE may detect a D2D monitoring period based on theD2D configuration information.

The UE receives a UL grant indicating a PUSCH transmission from the BSin operation S2210. The UL grant may indicate the PUSCH transmissionusing first timing.

The UE transmits a PUSCH to the BS with the first timing based on the ULgrant in operation S2220. A PHICH that carries (or indicates) HARQACK/NACK with respect to the PUSCH may be transmitted from the BS with asecond timing.

Subsequently, a D2D monitoring period for detecting a D2D transmittedfrom another D2D UE may overlap the second timing. In this instance, theUE expects reception of a D2D signal, and may not expect reception of aPHICH. That is, the UE does not receive the PHICH, determines HARQACK/NACK with respect to the PUSCH according to the determined standard,and performs a UL HARQ operation based on the determination in operationS2230.

For example, when the D2D monitoring period and second timing overlap,it may be determined that the corresponding PHICH indicates ACK. In thisinstance, the physical layer of the UE does not expect reception of aPHICH in a DL subframe of the corresponding second timing, and maytransfer an ACK signal with respect to a transmission block (TB)associated with the PUSCH to a higher layer, e.g., MAC layer, (alt 1-1).Alternatively, when a MAC PDU for the corresponding PUSCH transmissionis not obtained from an Msg3 buffer, the MAC layer (or MAC entity) ofthe UE may set “HARQ_FEEDBACK”, which is a state variable associatedwith a HARQ process of the corresponding UE, to ACK (alt 1-2).

As another example, when the D2D monitoring period and the second timingoverlap, it may be determined that the corresponding PHICH indicatesNACK. In this instance, the physical layer of the UE does not expectreception of a PHICH in a DL subframe of the corresponding secondtiming, and may transfer a NACK signal with respect to a transmissionblock (TB) associated with the PUSCH to a higher layer, e.g., MAC layer,(alt 2-1). Alternatively, when a MAC PDU for the corresponding PUSCHtransmission is not obtained from an Msg3 buffer, the MAC layer (or MACentity) may indicate/perform a non-adaptive retransmission of thecorresponding PUSCH using timing determined by the HARQ entity (alt2-2).

FIG. 23 is a block diagram illustrating an example of another UEaccording to the present disclosure.

Referring to FIG. 23, a UE 2300 includes a receiving unit 2305, a UEprocessor 2310, and a UE transmitting unit 2320. The UE may furtherinclude a memory (not illustrated). The memory is connected with the UEprocessor 2310, and stores various pieces of information for driving theUE processor 2310. In the above described embodiments, the operations ofthe UE 2300 may be implemented under the control of the UE processor2310. Particularly, the UE processor 2310 includes a data processingunit 2311, a collision determining unit 2312, and a HARQ processing unit2313.

The UE receiving unit 2305 receives D2D configuration information from aBS 2350.

The UE receiving unit 2305 may receive a D2D signal transmitted fromanother D2D UE. Also, the UE receiving unit 2305 may receive a UL grantand a PHICH transmitted from the BS 2350.

The data processing unit 2311 generates a PUSCH based on the UL grant,and transmits the generated PUSCH to the BS through the UE transmittingunit 2320 using first timing.

The HARQ processing unit 2313 determines that a HARQ ACK/NACK signalwith respect to the PUSCH may be transmitted from the BS using secondtiming, and controls the UE receiving unit 2305. The UE receiving unit2305 may receive the HARQ ACK/NACK signal through the PHICH.

The collision determining unit 2312 may detect a D2D monitoring periodbased on the D2D configuration information. The collision determiningunit 2312 determines whether a timepoint corresponding to the secondtiming at which the PHICH is transmitted from the BS 2350 and the D2Dmonitoring period overlap in the time axis. When the second timing andD2D monitoring period overlap, the collision determining unit 2312controls the UE receiving unit 2305 to preferentially receive a D2Dsignal of the D2D monitoring period. That is, in this instance, thecollision determining unit 2312 expects reception of a D2D signal, anddoes not expect reception of a PHICH.

When the second timing and D2D monitoring period overlap and the UEreceiving unit 2305 does not receive a PHICH, the HARQ processing unit2313 determines HARQ ACK/NACK with respect to the PUSCH according to apredetermined rule, and performs a UL HARQ operation based on thedetermination.

For example, when the D2D monitoring period and second timing overlap,the HARQ processing unit 2313 may determine that the corresponding PHICHindicates ACK. In this instance, the HARQ processing unit 2313 maycontrol the physical layer to transfer an ACK signal with respect to atransmission block (TB) associated with the PUSCH to a higher layer,e.g., MAC layer, (alt 1-1). Alternatively, when a MAC PDU for thecorresponding PUSCH transmission is not obtained from an Msg3 buffer,the HARQ processing unit 2313 may control the MAC layer (or MAC entity)to set “HARQ_FEEDBACK”, which is a state variable associated with a HARQprocess of the corresponding UE, to ACK (alt 1-2).

As another example, when the D2D monitoring period and the second timingoverlap, the HARQ processing unit 2313 may determine that thecorresponding PHICH indicates NACK. In this instance, the HARQprocessing unit 2313 may control the physical layer to transfer a NACKsignal with respect to a transmission block (TB) associated with thePUSCH to a higher layer (MAC layer). Alternatively, when a MAC PDU forthe corresponding PUSCH transmission is not obtained from an Msg3buffer, the HARQ processing unit 2313 may control the MAC layer (or MACentity) to indicate/perform a non-adaptive retransmission of thecorresponding PUSCH using determined timing through the HARQ entity.

The BS 2350 includes a BS transmitting unit 2355, a BS processor 2360,and a BS receiving unit 2370. The BS 2350 may further include a memory(not illustrated). The memory may be connected with the BS processor2360, and may store various pieces of information for driving the BSprocessor 2360. The operations of the BS 2350 in the above describedembodiments may be implemented under the control of the BS processor2360. The BS processor 2360 includes an RRC connection determining unit2361, a D2D resource allocating unit 2362, a D2D mode setting unit 2363,a scheduling unit 2364, and a HARQ processing unit 2365.

The BS transmitting unit 2355 transmits D2D configuration information tothe UE 2300. The BS transmitting unit 2355 transmits a UL grant to theUE 2300. The BS transmitting unit 2355 transmits a PHICH to the UE 2300.

The BS receiving unit 2370 receives a PUSCH from the UE 2300.

The RRC connection determining unit 2361 may determine whether the UE2300 is an idle mode or an RRC-connected mode.

The HARQ processing unit 2365 determines whether the BS receiving unit2370 successfully receives a PUSCH, and generates HARQ ACK/NACKinformation. The BS transmitting unit 2355 may transmit the HARQACK/NACK information to a UE through a PHICH.

The D2D mode setting unit 2363 may set a D2D mode of the UE 2300.

The D2D resource allocating unit 2362 may generate informationassociated with a resource pool for D2D communication based on whetherthe UE 2300 is in an idle mode or an RRC-connected mode. Also, the D2Dresource allocating unit 2362 generates D2D configuration information.The D2D configuration information may include information associatedwith a D2D monitoring period (resource monitoring information). The D2Dconfiguration information may include information associated with a D2Dresource pool for D2D mode 2. The resource monitoring information mayinclude only information associated with a period for monitoring D2Dsignals of D2D UEs that access a single operator's network, or may alsoinclude information associated with a period for monitoring D2D signalsof D2D UEs that access a different operator's network.

What is claimed is:
 1. A method comprising: establishing connectionswith a first carrier and a second carrier; determining, by a userdevice, a time period for a wireless communication between user devices,wherein the wireless communication between user devices is associatedwith the second carrier; receiving, by the user device and via the firstcarrier, an uplink grant in subframe n; determining, by the user deviceand based on the uplink grant received via the first carrier, a firstsubframe associated with an uplink signal to a base station associatedwith the first carrier; based on determining that the first subframeoverlaps in time with the time period, refraining from transmitting theuplink signal in the first subframe; and transmitting, based on areception timing of the uplink grant and based on a non-adaptiveretransmission, the uplink signal in subframe n+12, wherein the firstsubframe corresponds to subframe n+4.
 2. The method of claim 1, whereinthe uplink signal comprises Hybrid Automatic Repeat Request (HARD)feedback.
 3. The method of claim 1, wherein the time period comprises aplurality of subframes associated with the second carrier.
 4. A methodof transmitting uplink data, the method comprising: determining, by auser device, a time period for monitoring a wireless communicationbetween user devices; determining, by the user device, a first subframeassociated with a Hybrid Automatic Repeat Request (HARQ) feedbackreception; and based on whether the first subframe overlaps in time withthe time period, setting a state variable associated with the HARQfeedback reception to acknowledgement.
 5. The method of claim 4, whereinsetting the state variable associated with the HARQ feedback receptionto acknowledgement comprises: based on determining that the firstsubframe overlaps in time with the time period and determining that aMedia Access Control Protocol Data Unit (MAC PDU) was not obtained froma Message3 buffer, setting, by a MAC entity of the user device, thestate variable associated with the HARQ feedback reception toacknowledgement.
 6. The method of claim 5, wherein the MAC entity of theuser device sets the state variable associated with the HARQ feedbackreception to acknowledgement without confirming acknowledgementinformation of the HARQ feedback reception scheduled to be received inthe first subframe.
 7. A user device comprising: a transmitter; one ormore processors; and memory storing instructions that, when executed,cause the user device to: establish connections with a first carrier anda second carrier; determine a time period for a wireless communicationbetween user devices, wherein the wireless communication between userdevices is associated with the second carrier; receive, via the firstcarrier, an uplink grant in subframe n; determine, based on the uplinkgrant received via the first carrier, a first subframe associated withan uplink signal to a base station associated with the first carrier;based on determining that the first subframe overlaps in time with thetime period, refrain from transmitting the uplink signal in the firstsubframe; and  control the transmitter to transmit, based on a receptiontiming of the uplink grant and based on a non-adaptive retransmission,the uplink signal in subframe n+12, wherein the first subframecorresponds to subframe n+4.
 8. The user device of claim 7, wherein theuplink signal comprises Hybrid Automatic Repeat Request (HARQ) feedback.9. The user device of claim 7, wherein the time period comprises aplurality of subframes associated with the second carrier.
 10. A userdevice of transmitting uplink data, the user device comprising: one ormore processors; and memory storing instructions that, when executed,cause the user device to: determine a time period for monitoring awireless communication between user devices; determine a first subframeassociated with a Hybrid Automatic Repeat Request (HARQ) feedbackreception; and based on whether the first subframe overlaps in time withthe time period, set a state variable associated with the HARQ feedbackreception to acknowledgement.
 11. The user device of claim 10, whereinsetting the state variable associated with the HARQ feedback receptionto acknowledgement comprises: based on determining that the firstsubframe overlaps in time with the time period and determining that aMedia Access Control Protocol Data Unit (MAC PDU) was not obtained froma Message3 buffer, set, by a MAC entity of the user device, the statevariable associated with the HARQ feedback reception to acknowledgement.12. The user device of claim 11, wherein the MAC entity of the userdevice sets the state variable associated with the HARQ feedbackreception to acknowledgement without confirming acknowledgementinformation of the HARQ feedback reception scheduled to be received inthe first subframe.